1. Field of the Invention
The present invention relates to a phase control switching device for controlling switching time of a switching device for electrical power, such as a breaker, in consideration of residual magnetic flux of the core of a transformation device of electrical energy, such as a transformer or a shunt reactor, whereby occurrence of transient exciting incoming current caused by switching of the switching device, which is harmful to the transformation device connected to a power system, can be suppressed to the minimum level.
2. Description of the Related Art
There is known a phase control switching device in which when residual magnetic flux exists in the core of a transformer or the core of a shunt reactor, a transitional switch surge phenomenon is suppressed by estimating the residual magnetic flux of each phase of the transformer or shunt reactor and operating a breaker at the optimal throw-in timing corresponding to the residual magnetic flux of each phase (for example, JP-A-2001-218354 (see paragraph numbers [0004], [0007], [0008], FIGS. 1, 24).
In the conventional phase control switching device, it is assumed that breaking is carried out at a current zero point which occurs at an interval of an electrical degree of 60° in commercial frequency every phase when each breaker of three phases is opened, and thus the residual magnetic flux of the first breaking phase is equal to zero while the residual magnetic flux of the second breaking phase or third breaking phase is equal to +K or −K. Therefore, even when the closing operation of the breaker is controlled in consideration of the residual magnetic flux of each phase, there is a difference in residual magnetic flux value between a second throwing phase (for example, a phase of −K in residual magnetic flux) and a third throwing phase (for example, a phase of zero in residual magnetic flux) just after the first phase (for example, a phase of +K in residual magnetic flux) is thrown. Therefore, when the second throwing phase and the third throwing phase is thrown under this state, any one or both of the second throwing phase and the third throwing phase are thrown at an electrical degree at which the residual magnetic flux and the stationary magnetic flux are not coincident with each other. Therefore, a transitional phenomenon of magnetic flux occurs, and a DC magnetic flux is superposed on any one or both of the second throwing phase and the third throwing phase. Accordingly, there is a drawback that transitional exciting incoming current caused by switching of the switching device which is severe to a transformer cannot be suppressed to the minimum level when magnetic saturation occurs.